1. Field of the Invention
The present general inventive concept relates to a piezoelectric inkjet head, and more particularly, to a piezoelectric actuator of an inkjet head that has an improved structure such that a flexible printed circuit can be bonded to the piezoelectric actuator more reliably, and a method of forming the piezoelectric actuator of the inkjet head.
2. Description of the Related Art
Generally, inkjet heads are devices for printing a color image on a printing medium by ejecting ink droplets onto a desired region of the printing medium.
Depending on an ink ejecting method used by the inkjet heads, the inkjet heads can be classified as thermal inkjet heads and piezoelectric inkjet heads. The thermal inkjet head generates bubbles in the ink to be ejected using heat and ejects the ink by utilizing the expansion of the bubbles. On the other hand, the piezoelectric inkjet head ejects ink using pressure generated by deforming a piezoelectric material.
FIG. 1A is a partial plan view illustrating a conventional piezoelectric inkjet head, and FIG. 1B is a sectional view taken from line A-A′ of the conventional piezoelectric inkjet head of FIG. 1A.
Referring to FIGS. 1A and 1B, a manifold 11, a plurality of restrictors 12, and a plurality of pressure chambers 13 forming an ink flow channel are formed in a flow channel plate 10 of the inkjet head. A vibration plate 20 which can be deformed by piezoelectric actuators 40 is bonded to a top surface of the flow channel plate 10, and a nozzle plate 30 in which a plurality of nozzles 31 are formed is bonded to a bottom surface of the flow channel plate 10. The vibration plate 20 can be formed integrally with the flow channel plate 10, and the nozzle plate 30 can also be formed integrally with the flow channel plate 10.
The manifold 11 is an ink passage supplying ink from an ink reservoir (not illustrated) to the respective pressure chambers 13, and the restrictors 12 are ink passages allowing inflow of ink from the manifold 11 to the pressure chambers 13. The pressure chambers 13 are filled with the supplied ink and are arranged at one side or both sides of the manifold 11. The nozzles 31 are formed through the nozzle plate 30 and connected to the respective pressure chambers 13. The vibration plate 20 is bonded to the top surface of the flow channel plate 10 to cover the pressure chambers 13. The vibration plate 20 is deformed by an operation of the piezoelectric actuators 40 to change pressures in the respective pressure chambers 13 so as to eject ink from the ink chambers 13. Each of the piezoelectric actuators 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43 that are sequentially stacked on the vibration plate 20. The lower electrode 41 is formed along the entire surface of the vibration plate 20 as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 above each of the pressure chambers 13. The upper electrode 43 is formed on the piezoelectric layer 42 as a driving electrode for applying a voltage to the piezoelectric layer 42.
To apply a driving voltage to the piezoelectric actuator 40, a flexible printed circuit (FPC) 50 is connected to the upper electrode 43. In particular, the FPC 50 is placed on the piezoelectric actuators 40 with signal lines 51 of the FPC 50 in alignment with the upper electrodes 43 of the piezoelectric actuators 40, and then the signal lines 51 are bonded to top surfaces of the upper electrodes 43 by heating and pressing.
However, as illustrated in FIG. 1A, since the pressure chambers 13 are narrow and long, the piezoelectric layers 42 and the upper electrodes 43 are also narrow and long. Therefore, bonding regions between the upper electrodes 43 and the signal lines 51 must be sufficiently long for reliable bonding. For this reason, in the conventional inkjet head, the piezoelectric layers 42 and the upper electrodes 43 are substantially longer than the pressure chambers 13 (for example, two times longer than the pressure chambers 13), and the signal lines 51 of the FPC 50 are bonded to portions of the upper electrodes 43 that are not situated above the pressure chambers 13.
Although the piezoelectric layers 42 are not required to be longer than the pressure chambers 13 for changing the pressures of the pressure chambers 13, the piezoelectric layers 42 are formed to be much longer than the pressure chambers 13 for insulating the upper electrodes 43 from the lower electrode 41 and for supporting the upper electrodes 43. In this case, the capacitance, driving load, and response time of the piezoelectric actuators 40 are increased.
Further, since the piezoelectric layers 42 are long and narrow as described above, the upper electrodes 43 formed on the piezoelectric layers 42 should also be long and narrow. Therefore, when the FPC 50 and the upper electrodes 43 are slightly misaligned, the signal lines 51 of the FPC 50 will not be precisely bonded to the top surfaces of the upper electrodes 43, thereby causing bonding failure or decreasing bonding strength. If a bonding strength between the signal lines 51 of the FPC 50 and the upper electrodes 43 is weak, the inkjet head cannot be reliably used for a long time.